This paper focused on the relationship between periodontitis and Type 2 diabetes mellitus (T2DM). There is an abundance of evidence that diabetes mellitus play important etiological roles in periodontal diseases. In addition, periodontal diseases have powerful and multiple influences on the occurrence and severity of systemic conditions and diseases, such as diabetes mellitus, cardiovascular disease, respiratory disease and pregnancy complications. The relationship of periodontitis and diabetes has been supported by sufficient evidences in the past twenty years: (1) diabetes is an independent risk factor of chronic periodontitis; (2) metabolic control will improve the prognosis of chronic periodontitis; (3) the treatment of chronic periodontitis will improve the metabolic level. Our recent investigation on periodontal status in the families of type 2 diabetes mellitus further confirmed the relationship. It was showed that the periodontal index such as probing depth (PD), attachment loss (AL) and numbers of tooth loss in diabetes family members were significantly higher than non-diabetes family members, while no difference of periodontal parameters was found between well control family members and non diabetes family members. In the development of type 2 diabetes (T2DM) and its complications, the advanced glycation end products (AGEs) and its receptors were to be recognized as important factors. The distributions of AGEs and the receptor for AGEs (RAGE) are highly consistent in various tissues. One study in our laboratory demonstrated that RAGE was strongly expressed in gingival tissues gathered from T2DM patients with periodontitis compared with systemically healthy chronic periodontitis patients, the expression of RAGE was positively correlated with the expression of TNF-alpha, indicating that AGE-RAGE pathway was involved in the development of periodontitis in T2DM patients. It is known that inflammation could induce the prediabetic status characterized by insulin resistance and dyslipidemia. However, it is still unclear whether periodontitis is a risk factor of type 2 diabetes mellitus or not. In a current study, the effect of periodontitis on serum levels of lipid and glucose of aggressive periodontitis (AgP) patients was implied, as the average serum levels of triglycerides and glucose of a large number of AgP patients were both significantly higher than healthy control group, and serum level of total cholesterol in AgP group was positively associated with the percentage of severe attachment loss sites. It seems that periodontitis may alter serum lipid and glucose levels. Furthermore, the effect of periodontitis on diabetes in an animal study has also demonstrated that experimental moderate periodontitis as well as castration could induce insulin resistance and beta cell impairment in rats, and that combination of the two factors would aggravate the degree of insulin resistance (IR). In conclusion, interrelationship between periodontitis and diabetes has been further approved recently.